Burglarproof chain guard

ABSTRACT

A door guard for preventing unauthorized entry into a room. It utilizes a stationary anchor in the wall within the room adjacent to a doorknob. A chain secured to the anchor carries an enlarged ring at its outer end, which can be fitted over the doorknob. A protective sleeve is loosely mounted about the chain to prevent an intruder from cutting the chain links.

I O United States Patent 11 1 1111 3,853,343

Hunter Dec. 10, 1974 [5 BURGLARPROOF CHAIN GUARD 1,380,720 6/1921 Johnson 70/49 1 3,451,708 6/1969 Brooks 292/264 [75] Invent Hunter Smkana, wash- 3,531,955 10/1970 Taylor et a]. 70/18 [73] Assignee: Continental Lektroniks CorpQ,

Spokane Wash' Primary Examiner-Richard E. Moore 22 Filed; A 1 1973 Attorney, Agent, or FirmWells, St. John & Roberts [21] Appl.. No.: 352,050

- [57] ABSTRACT (gill. 292/26lg6E2c4/177Z33: A door guard for preventing unauthorized entry into a [58] Fieid 17 18 30 room. It utilizes a stationary anchor in the wall within 70/49 93 6 6 the room adjacent to a doorknob. A chain secured to 81 the anchor carries an enlarged ring at its outer end, which can be fitted over the doorknob. A protective sleeve is loosely mounted about the chain to prevent [56] UNITE S S FZfF ES SZQFENTS an intruder from cutting the chain links.

878,607 2/1908 Cairns 292/264 1 Claim, 2 Drawing Figures 1 BURGLARPROOF CHAIN GUARD BACKGROUND OFTl-IE INVENTION Mechanisms for securing doors against unwanted intruders vary from latches and bolts to many types of chain guards. The chain guard is specifically a device designed to secure the door to the door frame or wall so that when the door is opened, its movement or opening is restricted by the chain to prevent entry of an undesired person. The chain guard has the advantage over the latch or bolt in that by use of the chain guard, the

user may open the door to receive messages or documents without providing access to-the premises.

' A number of chain guards of varying designs are currently available. These may be catagorized as follows:

1. A chain secured to the door frame by a bracket and one or more small screws, and fastened or unfastened to a similar bracket screwed to the door.

2. The reverse of the above wherein the chain is secured to the door and fastened or unfastened to a bracket fastened to the door frame by one or more screws. 7

3. A chain secured to the door frame by a bracket with one or more screws and fastened to the door by looping the chain around the doorknob.

All of the above types of chain guards are ineffectual and all can be easily broken or cut because:

1. The chain is exposed to the intruder when the door is opened and can be cut with any type of cutting device or hacksaw.

2. All of these devices are secured at one end or the other or both by one or more small screws. These screws can be pulled loose yet cannot be larger because they are anchored into the thin skin of the door and are into the door molding which is not sufficiently heavy to accommodate larger screws. Furthermore, the molding itself will come loose from the wall when pressure is applied to the chain guard.

An example of a recent development in this type of chain guard is shown in the "Lentz U.S. Pat. No. 3,667,794. In this arrangement, the chain is anchored to the wall studding in such' a way as to prevent it from being pulled loose. The remaining end of the chain is fastened and unfastened to a special bracket secured to the door latch hardware. While it provides better security in that it is adequately anchored at each end, the device is very complicated and its installation is expensive. Furthermore, the brackets required for each end of the chain are different for each typeof wall and each type of door hardware .A very large .number of parts would be required to accomplishinstallation.

The present device is a chain guard designed to secure the door against unauthorized intrusion while still providing the user with the ability to open the ,door sufficiently to see, talk and receive documentsfrom the outside. It fits all doors having doorknobs and can be installed in the wall studding adjacent any door frame without special tools or training.

SUMMARY OF THE INVENTION The invention'comprises a burglarproof chain guard for a door that is mounted within a building wall for hingedmovement into a'room and having an'enlarged doorknob on a reduced doorknob stem. It includes a stationary anchor embedded into the wall adjacent to the doorknob when the door is closed. A metal ring having an inside diameter slightly greater than the doorknob diameter is mounted at one end of a chain. the other end of the chain being secured to the anchor. The ring can then be passed over the doorknob when the door is closed, but prevents substantial opening of the door'by its engagement against the reduced stem of the doorknob.

A first object of this invention is to provide a relatively inexpensive chain guard which will effectively prevent outside intrusion into a room where the chain guard is in use.

Another object of this invention is to provide an almost universal chain guard for all types of door frames and all types of door hardware.

Another object of this invention. is to minimize the skill and training required for installation of the chain guard. Furthermore, only a single aperture must be DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevation view showing thechain guard in use on a partially opened door;

FIG. 2 is a plan sectional view taken substantially along line 2-2 in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIGS. 1 and 2 illustrate the chain guard in assembly,

mounted on a partially opened door held in the illustrated position by engagement of the stem of the doorknob and edge of the door against the chain structure.

, The chain guard is composed of four component parts.

These comprise a welded steel ring 10, a welded steel chain 11, a steel sleeve 12, and an eye screw 13.

The device is illustrated as it would be used'within a room having a building wall 14 that includes a door frame 15. The numeral 16 indicates typical frame studding adjacent to the door frame 15. An interior wall structure in the form of gypsum board, plaster, tile,

paneling or other materials is indicated at 17. The door itself is indicated by the numeral 18. It is provided with a conventional latch 20 controlled by doorknobs 21, 22

respectively mounted on reduced diameter stems 23, 24.

It is well known that entry can be attained into most rooms by forcing the latch 20 on door 18. Additional protection in the past has been provided by barrel bolts or chain mounted between the door and door frame. A general discussion of these alternatives is contained in US. Pat. No. 3,667,794, referenced above. However, the present device minimizes expense in the production of the apparatus itself and its installation within any room adjacent to an exterior or interior door.

As can be seen from'the drawings, the eye screw 13 is threadably engaged within the wall studding 16, providing sufficient penetration into the studdingl6 to assure that it will not be pulled out in response to forces resulting from attempted opening of door 18. The steel sleeve 12 preferably has an exterior diameter of about three-fourths inch and protects chain. 11 from being cut by cutting tools or saws through the partially opened area between door 18 and frame 15. The length of sleeve 12 is slightly less then the length of chain 11, assuring free pivotal movement of the chain at both of its ends and contact of sleeve 12 by the opening edge of door 18. In a typical installation, chain 11 will have a nominal length of 4 /2 inches, and sleeve 12 will be 3 inches in length. Sleeve 12 should be at least one-half the length of chain 11 so that it always covers the majority of the chain links facing the opening between door 18 and frame 15.

The welded steel ring is typically of an inside diameter of 2 A inches to accommodate doorknobs of standard and non-standard design. In a typical arrangement, it would be fabricated of 3/16 inch diameter spring steel to provide sufficient to withstand the forces that would be exerted upon it.

The apparatus is easily installed by simply drilling a hole through the room wall adjacent to the doorknob and threadably mounting the eye screw 13 as a fixed anchor. The loosely pivoted chain 11 then permits ring 10 to be slipped over the enlarged interior doorknob '21, bringing it to rest on stem 23. The relatively short length of chain 11 prevents ring 10 from being moved over doorknob 21 when the door is ajar or partially open. The location of eye screw 13 must be such that ring 10 just clears the inner edge of doorknob 21 when the door is completely closed.

In this arrangement, the chain guard cannot be pulled loose because the chain is anchored permanently to the wall by a secure threaded arrangement and is secured to the door by use of the inside doorknob which cannot be broken off or pulled loose. The apparatus can easily be fabricated of materials having sufficient strength to prevent breakage by an intruder. The device cannot be cut because the exposed portion of chain 11 is protected by the steel sleeve 12. The dimensions of sleeve 12 must be such that the diameter of the sleeve is too large to fit into the jaws of a high leverage bolt cutter and the sleeves will not be cut by a hacksaw because it is free to rotate on chain 12. Insufficient room is provided to secure the chain against rotation and to insert a hacksaw at the same time.

Having thus described my invention, I claim:

1. A burglarproof chain guard for a door mounted within a building wall forhinged movement into a room and having an enlarged doorknob on a reduced support stem facing toward the room, comprising:

a stationary anchor embedded into the framework around the door opening within the room and adjacent to the doorknob when the door is closed;

a metal ring having an inside diameter slightly greater than the doorknob diameter to enable the ring to be passed over the doorknob and rest upon the stem thereof;

-a chain interconnecting the anchor and ring, the length of the chain being just adequate to permit the ring to pass over the doorknob when the door is closed; and

a straight cylindrical steel sleeve enclosing substantially the entire length of the chain within the sleeve and freely rotatable on the chain. 

1. A burglarproof chain guard for a door mounted within a building wall for hinged movement into a room and having an enlarged doorknob on a reduced support stem facing toward the room, comprising: a stationary anchor embedded into the framework around the door opening within the room and adjacent to the doorknob when the door is closed; a metal ring having an inside diameter slightly greater than the doorknob diameter to enable the ring to be passed over the doorknob and rest upon the stem thereof; a chain interconnecting the anchor and ring, the length of the chain being just adequate to permit the ring to pass over the doorknob when the door is closed; and a straight cylindrical steel sleeve enclosing substantially the entire length of the chain within the sleeve and freely rotatable on the chain. 